1. Field of the Invention
The present invention is directed to a gravel pack system, and more particularly to a gravel pack system which raises the crossover assembly within the screen assembly to position the system for each gravel pack operation.
2. Background of the Art
Sand flow from unconsolidated formations is controlled through chemical or mechanical means to prevent or correct a variety of potentially serious and costly problems, such as: production loss caused by sand bridging in casing, tubing and/or flow lines; failure of casing or liners due to the removal of surrounding formation, compaction and erosion; abrasion of downhole and surface equipment; and handling and disposal of unconsolidated materials from the recovered hydrocarbons. One mechanical means for correcting sand problems is the use of a gravel pack.
Gravel packing is a method of forming a filter of gravel between the oil, gas or water producing formation and the production pipe and if used in an uncased or open hole, will serve to support the unconsolidated formation. Normally, the production pipe is attached at its lower end to a section of pipe called a liner or screen which has been disposed adjacent the formation to be produced. The liner or screen has a plurality of narrow spaced apart slots or screen covered openings through which the formation fluids enter the production pipe from the formation. The body of gravel is interposed between the screen and the formation to serve as a filter to screen out the fine sand and the like as the well fluid flows from the formation into the screen so that the produced fluids may enter the production pipe free of the sand or unconsolidated material from the producing formation. Where the screen is set in an open hole, the gravel pack supports the unconsolidated formation. Where the screen is set inside a perforated casing, the gravel pack functions primarily as a filter with the casing assisting in supporting the unconsolidated formation.
In the completion of wells, it is known (1) to install a gravel pack assembly including a packer, liner and screen in the well casing adjacent the producing formation, and (2) to place gravel around the screen to a sufficient height to insure that the gravel will remain consolidated and not be displaced as it filters unconsolidated material out of the inflowing well fluid. The gravel is conducted down the well by a gravelling pipe string to the gravel pack assembly for placement outside the screen. A part of the operation is to apply pressure on the placed gravel or squeeze the gravel into the producing formation which contains or is producing unconsolidated material.
In a conventional gravel pack, the gravel pack assembly, including the hydraulic setting tool and crossover tool and the required screen and blank pipe, is run into the well. The packer is set using pump pressure applied to the pipe string. After the packer is seated, the crossover valve may be opened and closed by raising and lowering the crossover tool to carry out the gravelling operation. With the crossover valve closed, the packer may be pressure tested by pumping down the casing. Pumping down the pipe string and into the formation is done to establish an injection rate. The formation may be acidized or otherwise treated if needed. With the crossover valve open, a gravel slurry may be circulated to place the gravel outside the screen and into the formation until an adequate gravel pack is obtained. If desired, the crossover valve may be closed to apply pressure to the placed gravel and obtain a conventional squeeze pack. The excess slurry in the pipe string is removed by reverse circulation with the gravel packed formation isolated. This isolated formation provides a more positive means of excess slurry removal and helps protect the formation from circulation pressure and possible loss of circulation fluid. After the removal of the setting tool and crossover tool, a production packer seal assembly is left in the well for production of the formation.
An optional wire line-set sump packer may be utilized to provide a well bottom space for the settlement of fines produced or possible loss of wire line tools. The wire line-set sump packer also serves to locate the screen properly with reference to the perforations in the casing. Although sump packers are often used, alternatives include cement bottoms, bridge plugs or retainer bottoms.
Gravel packing wells involves a complicated series of tool movements to effectively place gravel around the screen and into the perforations. This multi-position approach to gravel packing has been perfected in recent years, and the results indicate improved pack performance. Almost all such gravel packs, however, have been done from a stationary surface, i.e. a land rig or a platform rig.
Special problems are posed with gravel packing from a floating vessel. Floating rigs and semi-submersibles have greatly increased the water depth for offshore exploration and production. Floating rigs can drill in water depths which cannot be reached by conventional jack-up rigs. Although much of the work done on floating rigs is exploration, some well completions are now being performed.
Floating rigs or semi-submersibles do not rest on the ocean bottom but float on the surface of the water. They are held in place by various anchoring systems and will move with the sea waves. The heaving or up and down movement of the floating rigs caused by the waves will vary depending upon the physical characteristic of the wave and the sea environment. Heave may vary from a few inches to thirty or forty feet in harsher environments. The speed at which the rig moves will be dependent upon the wave frequency.
If the pipe string extending to the subsea well is suspended from a floating rig, the string will move in response to the heave of the waves and the motion of the floating rig. To prevent the pipe string from varying in tension and compression due to the wave movement, compensators have been developed to permit the floating rig to move in response to the waves but yet cause a predetermined amount of weight to be placed on the block suspending the pipe string. This will permit the pipe string to be relatively stationary as the rig moves up and down in response to the ocean waves. The compensator is set for a predetermined total weight of the pipe string. As the rig moves up and down, the compensator adjusts to the friction resistance of the pipe being pulled through the fluid in the well bore. This friction force increases or decreases with the pipe weight, and the compensator adjusts to cause the pipe weight to be maintained at a prescribed level. This tends to dampen the pipe movement and causes it to be less than the movement of the rig.
In a conventional gravel pack, the packer is set and the crossover tool is released from the screen assembly so that it can then be moved to the various positions required for performing the gravel pack. During this positioning operation, the crossover tool is suspended on the work string. If conventional gravel pack tools are used on floating rigs, the movement of the rig is transmitted to the crossover tool during the positioning operation which causes the crossover tool to oscillate between positions causing problems in the gravelling operation.
When a gravel pack operation is attempted from a floating rig using a conventional gravel pack system, difficulty is experienced in determining with certainty that the gravel pack is deposited at the proper location relative to the formation. When gravel packing is between a screen and a casing having perforations opposite the producing formation, precise location of the gravel pack is especially important because the length of the perforated section of the casing will often be quite short and at great depths.
Unless the positioning of the crossover tool through which the gravel packing must be conducted is known and controlled, premature bridging by the gravel slurry often will occur at points above the desired location, e.g. between a screen and a casing, so that production is interfered with and ineffective support of the formation will occur. Moreover, with conventional gravel pack systems, no good indication can be obtained to apprise the operator that such bridging has occurred or as to its location relative to the producing formation.
U.S. Pat. No. 3,062,284 discloses a method for gravel packing a well. The specific apparatus employed is run into the well on a tool string to a point in which seals of the tool will be somewhat above the producing formation which is to be gravel packed. With the seals actuated and wash fluid, such as water or oil, being pumped down the operating string, the seals prevent the return flow of the fluid which results in back pressure being built up on the surface pump. Evidence of the build up of the pressure apprises the operator that the lower seal is above the perforations in the casing in a location of the gravel pack. Thereafter the tool string is lowered and the seal passes below the uncovered perforations in the casing which permits a washing operation to take place. The washing operation is continued with the tool string being lowered in short increments until the seal now is below all of the perforations in the casing. At this point of the operation, the return of fluids causes a back pressure in the pump. The operating string is then raised and lowered to set a liner hanger which is followed by raising the operating pipe while circulating a slurry of gravel. The operating pipe is elevated in short increments to progressively uncover the perforations providing a layering effect of the gravel as the operating pipe is raised. This method essentially has the two steps of washing and circulating a gravel slurry.
U.S. Pat. No. 4,474,239 discloses a method and apparatus for sand placement. The sand placement tool which is run into a well on a tubing provides an operation wherein the casing/tubing annulus is filled from the top down as compared to conventional tools and method where the casing/tubing annulus is filled from the bottom up.
U.S. Pat. No. 4,540,051 discloses a method and apparatus for gravel packing a cased well. The apparatus of this patent provides for the perforation of the casing at a production zone in a well and the subsequent gravel packing of a liner, screen or other filtering means positioned adjacent to the casing perforations with a single trip of the required apparatus into the well.
U.S. Pat. No. 4,541,486 is also directed to an apparatus which provides for the perforation of the casing at a production zone in a well and the subsequent gravel packing of a liner, screen, or other filtering means positioned adjacent to the casing perforations with a single trip of the required apparatus into the well.
U.S. Pat. No. 4,566,538 is directed to a method and apparatus for effecting the fail-safe perforating of a well casing. This patent is also related to the foregoing two patents.
Completion Services, Inc. of Lafayette, La., has a gravel pack system which is described in a brochure entitled "The Complete Gravel Pack" which is incorporated herein in its entirety by reference. The gravel pack system as described in this brochure is made up of a setting tool and crossover assembly and a liner and screen assembly. The liner and screen assembly of that system is made up of the following: a packer at the top of the assembly, a slotted perforated extension, a lower seal bore, an extension of pipe, a single interference collar, an extension of pipe, a production screen, and an O-ring sub and a tell tale screen below the production screen. Furthermore, there may be a sump-packer at the very bottom of the liner and screen assembly. Within the liner and screen assembly is a crossover assembly. The crossover assembly has an upper crossover section which includes an inner tube with a lower port which permits the fluid being injected into the tubing to be forced downwardly through the lower port and slotted perforated extension of the packer assembly to the producing area. The crossover assembly has at the lower end, a wash pipe connected to the upper crossover section for passage of fluid upwardly through the wash pipe and through an outer tube of the crossover section which has an upper port. The crossover assembly has seals around the periphery, at least one of which is above the upper port, and when seated within the seal bore of the upper packer of the liner and screen assembly, the seals close the upper port. The cooperating structure of the upper port, the seal above the port and the seal bore act as a valve for controlling the upward passage of fluid and thus function as a crossover valve. The liner and screen assembly and crossover assembly of this gravel pack system has a single crossover valve which is closed when the seal above the upper port of the crossover assembly is in contact with the seal bore of the packer and is opened when the crossover assembly is raised removing the seal from contact with the seal bore of the packer. In the operation of this gravel pack system the crossover assembly is sequentially raised opening the crossover valve and lowered a considerable distance to close this valve. This gravel pack system has great adaptability from a fixed rig. However, employing such a gravel pack system from a drilling vessel in constant motion caused by the waves, being raised and lowered in the water or heaving, the certainty of whether the crossover valve is open or closed cannot be determined and there is no compensation device or system to assure operational control.
According to the present invention, the gravel pack system provides structure which enables raising the crossover assembly to a fixed position within the screen assembly for each desired operation. Since the crossover tool becomes fixed before each operation, the fact that the operation is being carried out from a drilling vessel which has a constant heaving motion does not change the certainty of the position of the crossover tool within the well, and accordingly, the desired operation is carried out with the certainty that the system is in the desired position.
Conventional gravel packs require the pipe to be lowered following a circulating position to a squeeze position. The present invention does not require this, therefore minimizing the chance of sticking the crossover tool within the sand slurry. Lowering the pipe from one position to another while sand slurry is present in the crossover can cause a jamming effect between the crossover and seal or packer bore. The all up procedure of the present invention will minimize this deficiency.
Other more specific objects and advantages of the present invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawings illustrating the embodiments in accordance with this invention.